Primary related art of the present invention is found as a seal device shown in FIG. 13 (for example, see Japanese Utilities Laid-open Publication No.H1-98368 or U.S. Pat. No. 4,844,483). This seal device 100 is applicable to a drive wheel apparatus of a mining damp truck.
The seal device 100 is arranged as shown in FIG. 13. The seal device 100 of FIG. 13 displays a cross sectional view of a half portion thereof being mounted to a drive wheel apparatus. In FIG. 13, a shaft (not shown) is disposed within a through hole of a fixed side retainer 130. There is disposed the seal device 100 in a cavity 120 which is formed between the shaft and the fixed side retainer 130. This deal device 100 protects the cavity 120 defined by the shaft and the fixed side retainer 130 against the attack by a sealed fluid M from outside A such as water, sludge or the like containing small particles like sands or the like.
In the seal device 100, a first seal ring 105 having a seal surface 105S and a second seal ring 115 having an opposed seal surface 115S not only face to each other surrounding the shaft, but the seal surface 105S and the opposed seal surface 115S are pressed against each other. In order to assure a sealing contact between the seal surface 105S on the first seal ring 105 and the opposed seal surface 115S on the second seal ring 115, the periphery of the first seal ring 105 is formed by a first tapered surface 105A, a first arcuate surface 105B and a first vertical surface 105C. Likewise, the periphery of the second seal ring 115 is formed by a second tapered surface 115A, a second arcuate surface 115B and a second vertical surface 115C.
Next, a first support surface 130A on the fixed side retainer 130 forms a shoulder surface, which defines one side wall of the cavity 120. Likewise, a second support surface 140A on a rotary side retainer 140 also forms another shoulder surface. Then the first seal ring 105, the second seal ring 115, the fixed side retainer 130 and the rotary side retainer 140 defines the cavity 120 therewithin.
There is disposed a first O-ring 102 near the cavity 120 side between the first tapered surface 105A and the first support surface 130A. Likewise, there is disposed a second O-ring 103 between the second tapered surface 115A and the second support surface 140A. The first O-ring 102 undergoes elastic deformation to form an elliptic cross section, which brings a first contact surface 102B into contact with the first tapered surface 105A while a second contact surface 102C is pressed against the first support surface 130A. Moreover, the second O-ring 103 also undergoes elastic deformation to form an elliptic shape after the first contact surface 103B comes into contact with the second tapered surface 115A and the second contact surface 103C is pressed against the second support surface 140A.
In the seal device 100 configured as described above, the first seal ring 105 is urged in the axial direction by the elastic deformation force of the first O-ring 102 while the second seal ring 115 also is urged in the axial direction opposing to the first seal ring 105 by a similar urging force due to the second O-ring 103. And the seal surface 105A and the opposed seal surface 115A slide to each other while maintaining tight contact thereof. When a sealed fluid M containing impurity reaches the cavity 120 from outside A, the pressure of the sealed fluid M creates urging forces onto the first O-ring 102 and the second O-ring 103 as well as onto the first seal ring 105 and the second seal ring 115 as illustrated in FIG. 3. The pressure of the sealed fluid M then act on the first vertical surface 105C and the second vertical surface 115C so that the pair of the seal surface 105A and the opposed seal surface 115A are pressed against each other by a large pressure which exceeds a prescribed value. Therefore, the seal surface 105A and the opposed seal surface 115A are forced to slide to each other under an intense press contact, which leads to a high temperature due to slide friction.
According to the experiments, when dirt water enters the cavity 120 impurities such as dirt and sand particles contained in the fluid are accumulated in the cavity 120. This cumulative pressure causes an urging pressure to the first vertical surface 105C on the first seal ring 105 and the second vertical surface 115C on the second seal ring 115 in mutually opposing directions, and friction heat generated by the sliding between the seal surface 105A and the opposing seal surface 115A sometimes increases the temperature of the respective seal rings 105, 115 to more than 300 degrees Celsius. When the first seal ring 105 and the second seal ring 115 are heated too much due to the heat generated during the sliding motion, rubber-made first O-ring 102 and second O-ring 103 get softened by the high temperature and fail to restore elastically to their original states. Therefore the first O-ring 102 and the second O-ring 103 are likely to diminish their ability of providing resiliently urging forces against the first seal ring 105 and the second seal ring 115, respectively. Further, the high temperature deteriorates the seal surface 105A and the opposing seal surface 115A and accelerates wear thereof.
Moreover, a floating seal device 150 shown in FIG. 14 is a second prior art related to the current invention (for example, see Utilities Public S62-4665 (pages 1 through 5, FIG. 5) or Patent Public 2002-98326, or the like).
This floating seal device 150 is so arranged that a first seal ring 152 and a second seal ring 153 which surround a drive shaft (not shown) substantially extend to the radial direction and face to each other on the slant. A seal surface 152A of the first seal ring 152 and a seal surface 153A of the second seal ring 153 are kept in sealing contact. The seal contact between the seal surface 152A of the first seal ring 152 and the seal surface 153A of the second seal ring 153 is urged by the compression force which is caused by the elastic deformation of a rubber-made first O-ring 155 and a second O-ring 156 to an elliptic cross section form. For that purpose, the first O-ring 155 and the second O-ring 156 are disposed, respectively, between a first casing 160 and the first seal ring 152 and between a second casing 170 and the second seal ring 153 in such a way that the O-rings face to each other while forming an angle to the radial direction. A first seal tight surface 155A is pressed against a first support surface 160A while a second seal tight surface 156A is pressed against a second support surface 170A. Further, a first seal tight surface 155B is pressed against the first seal ring 152 while a second seal tight surface 156B is pressed against the second seal ring 153.
This floating seal device 150 provides a seal against a high pressure sealed fluid M containing slurry. It also effects a seal against a fluid M containing fine particles. High pressure of the sealed fluid M which breaks in from outside A causes a squeeze on the rubber material of the first O-ring 155 and the second O-ring 156 which are arranged in a symmetric location, and that intensifies the press contact between the seal surfaces 152A and 153A of the first seal ring 152 and the second seal ring 153, respectively. Significant resilient compression forces caused by the first O-ring 155 and the second O-ring 156 also intensify a press contact between the respective seal surfaces 152A and 153A, and thereby wear of the seal surfaces 152A and 153A is accelerated.
When the sealed fluid M comes into the cavity 160 from outside A and exerts pressure onto the second O-ring 156 and the second seal ring 153 as well as the first O-ring 155 and the first seal ring 152, slurry trapped between the first O-ring 155 and the first seal ring 152 and between the second O-ring 156 and the second seal ring 153, respectively, give pressure to the first O-ring 155 and the second O-ring 156 in radially inward a direction, and the respective seal surfaces 152A, 153A are deviated from a parallel relationship relative to each other since the first O-ring 155 and the second O-ring 156 are made of rubber material. Such a departure from the parallel relationship of the respective seal surfaces 152A, 153A causes uneven wear of the seal surfaces 152A, 153A. Also the respective pressure receiving areas disposed on radially outward side of the tapered surfaces 152B on the first seal ring 152 and the tapered surface 153B on the second seal ring 153 are increased by the deviations of the first O-ring 155 and the second O-ring 156, and the pressure by the slurry therefore urges the pressure receiving surfaces of the respective tapered surfaces 152B, 153B and causes wear of the respective seal surfaces 152A, 153A which slide against each other under the press contact. Moreover, the sliding frictional heat of the first seal ring 152 and the second seal ring 153 causes softening and stress relaxation of the first O-ring 155 and the second O-ring 156, and decreases resilient urging forces of the first O-ring 155 and the second O-ring 156.
The present invention is introduced to alleviate the above mentioned problems. A primary technical goal which this invention tries to achieve is to prevent wear of respective seal surfaces under the influence of a sealed fluid at high pressure or containing impurities. Further, stress relaxation in the respective resilient seal rings due to heat emitted during sliding of the respective seal surfaces is prevented and the resilient seal rings can exhibit outstanding resilient performance for urging the seal rings.